The present invention relates to a writing instrument having a structure in which inhibition of vaporization of an ink solvent is incomplete, which is equipped with an exchangeable inner pen (refill) filled with an ink which has a pen tip comprising a fiber feeder or a plastic feeder, particularly to a writing instrument suited to a marking pen, a white board marker and a felt-tip pen.
A large variety of writing instruments of a refill type has so far been put to practical use for ballpoint pens. In ballpoint pens, inks contain solvents having a low vapor pressure and have a high viscosity, and therefore the inks are less liable to volatilize. Further, the ballpoint pens have a structure in which a refill is less degraded and the refill can be exchanged.
In contrast with this, in markers called marking pens as a common name in which a pen tip comprises a fiber feeder comprising a fiber bundle or a plastic feeder, the following problem is present when markers of a refill type are put to practical use (actualize).
That is, as a principle, use of a solvent having a low vapor pressure (less liable to volatize) makes it possible to actualize marking pens of a refill type requiring no cap or having a structure in which a refill is incompletely sealed, but they have the problem that a drawn line-drying property which is a characteristic of a marking pen is damaged, so that the drawn lines are less liable to be dried.
When a solvent having a high vapor pressure (liable to volatize) is used, the drawn line-drying property is good, but if a writing instrument main body (external structure) in which a refill is mounted is not provided with a structure for sufficiently inhibiting a solvent from vaporizing, generated is a problem that a viscosity of an ink (particularly, a surface and an inside of a pen feeder) is elevated due to volatilization of the solvent, which makes writing impossible.
Known as a writing instrument in which a writing instrument main body is provided with a structure for preventing a solvent from vaporizing are, for example, a knock type writing instrument 44 as shown in FIGS. 4(a) and (b), in which a cap part 42 for a housing room 41 for housing a pen tip 40 covers the room when the pen tip is drawn in by a string member 43 to be movable with knocking operation (U.S. Pat. No. 2,579,188, Japanese Patent Application Laid-Open No. 81094/1998, Japanese Patent Application Laid-Open No. 81095/1998 and Japanese Patent Application Laid-Open No. 242094/1995), a knock type writing instrument 49 as shown in FIGS. 5(a) and (b), in which a housing room 48 for preventing a pen tip 46 from drying is provided in a writing instrument main body 45 which is covered by a rubber member 47 having a slit 47a (Japanese Utility Model Application Laid-Open No. 95288/1991) and a knock type writing instrument 54 as shown in FIGS. 6(a) and (b), in which a sealing member 53 having a slit 53a for preventing a pen tip 52 from drying is provided in a front barrel 51 of a writing instrument main body 50 (Japanese Utility Model Application Laid-Open No. 76778/1983). It is considered that writing instruments provided with sealing structures having these dry-preventing mechanisms can solve the problems described above, but if they are provided with both of a sealing structure and a structure which enables refilling, the structure is complicated more and more, and the product becomes more expensive. In addition thereto, it becomes more difficult to secure the sealing property. Further, a problem resides in that a simple structure using an elastic body shown in FIGS. 5 and 6 not only makes the initial performance imperfect but also makes it impossible to secure sufficient sealing due to deterioration of the elastic body with passage of time to cause inferior writing.
On the other hand, the followings have so far been carried out in order to obtain writing instruments such as marking pens, felt-tip pens and writing brush pens which are excellent in a cap-off performance for inhibiting pen tips from drying; that is, higher fatty acid esters of polyglycerin are added to inks (Japanese Patent Publication No. 34352/1987); paraffin waxes which can be deposited on the surface of a pen tip to form a thin film are added to inks (Japanese Patent Publication No. 35028/1989); hexaglyceryl tristearate is added to inks (Japanese Patent Application Laid-Open No. 232277/1990); and lecithin is added to inks (U.S. Pat. No. 2,594,457).
However, additives having a high vaporization-inhibiting effect have a low solubility (10% by weight or less) in solvents in many cases, and a problem resides in the fact that the solubility is low, particularly that the solubility at 0xc2x0 C. is very low (5% by weight or less). Involved therein is the problem that depositions of the additives described above are produced in the inks during storing at a low temperature or in repeating of low and high temperatures to cause clogging in the ink passages, whereby the writing property is reduced or the cap-off performance is deteriorated with the passage of time, and thus the effective vaporization-inhibiting effect has not yet been obtained.
On the other hand, disclosed in Japanese Patent Application Laid-Open No. 242094/1995 is a method of preventing drying for a writing instrument characterized by that in order to effectively inhibit vaporization of an ink solvent from a writing part during a period passing until initial writing after producing a writing instrument and to prevent it in a state not to be used over a long period of time from producing a cause of inferior writing, a high boiling solvent such as benzyl alcohol having a low volatilizing velocity out of ink solvents is in advance coated on or impregnated into the writing part of the writing feeder described below in a writing instrument in which one end part of a writing feeder prepared from a porous feeder material is inserted into an ink reservoir occuluding an ink prepared by dissolving a dye in a solvent and in which the other end part forms a writing part.
However, in the method of preventing drying for a writing instrument disclosed in this official gazette, an object thereof is to prevent drying during a period passing until initial writing after producing a writing instrument, and used is a high boiling solvent such as benzyl alcohol having a low volatilizing velocity out of ink solvents. Accordingly, it is not intended to prevent the writing part from drying after writing.
That is, a problem resides in that benzyl alcohol is liquid at room temperature and arbitrarily miscible with solvents so that it is occluded into an ink reservoir by virtue of diffusion of the solution to almost lose effect, if the pens are left standing over a long period of time. Further, benzyl alcohol flows out in writing once and therefore does not maintain the effect until the ink is exhausted.
As described above, the current situation is that in writing instruments such as marking pens, felt-tip pens and writing brush pens having pen tips comprising conventional fiber feeders or plastic feeders, the pen tips have not yet been sufficiently inhibited from drying, and the circumstance is that markers such as marking pens of a refill type have not been able to be provided as yet.
In light of the problems on the conventional techniques described above, the present invention intends to solve them, and an object thereof is to provide a writing instrument equipped with an exchangeable inner pen (refill) filled with an ink which has a pen tip comprising a fiber feeder or a plastic feeder, wherein it is excellent in inhibition of vaporization of an ink solvent from a pen tip; even if the writing instrument main body has a structure in which inhibition of vaporization of the ink solvent is insufficient or particularly the writing instrument does not have a cap member, the inner pen (refill) is less deteriorated and exchangeable; and it well adapts to an environmental issues such as the best utilization of the resources and can achieve a reduction in the cost.
Intensive investigations of the problems on the conventional techniques described above repeated by the present inventors have resulted in finding that in order to achieve a writing instrument such as a marking pen, a felt-tip pen and a writing brush pen which is excellent in inhibition of vaporization of an ink solvent from a pen tip and which is equipped with an exchangeable inner pen (refill) filled with an ink which has a pen tip comprising a fiber feeder or a plastic feeder and has a structure in which inhibition of vaporization of an ink solvent is incomplete, effective is coating the pen tip comprising a fiber feeder or a plastic feeder with a substance which is less liable to be dissolved in a solvent and has a vaporization-inhibiting action. Thus, the present invention has come to be completed.
That is, the writing instrument of the present invention having an excellent vaporization-inhibiting performance comprises the following items (1) to (6). (1) A writing instrument equipped with an exchangeable inner pen filled with an ink containing a solvent having a vapor pressure of 1 to 50 mm Hg (20xc2x0 C.) in a writing instrument main body which is a barrel part, wherein the inner pen described above has a pen tip comprising a fiber feeder or a plastic feeder, and the above pen tip is coated with a substance having a vaporization-inhibiting action, which forms a film that is always regenerated and broken in writing.
(2) The writing instrument as described in the above item (1), wherein the ink further comprises a substance having a vaporization-inhibiting action.
(3) The writing instrument as described in the above item (1) or (2), wherein the substance having a vaporization-inhibiting action is solid at room temperature and has a solubility of 10% by weight or less in an organic solvent at room temperature.
(4) The writing instrument as described in the above item (3), wherein the substance having a vaporization-inhibiting action has a melting point of 40 to 95xc2x0 C.
(5) The writing instrument as described in the above item (3), wherein the substance having a vaporization-inhibiting action is at least one selected from the group consisting of glycerin derivatives, alkyl phosphates, polyoxyethylenesorbitan fatty acid esters, polyoxyethylenesorbit fatty acid esters, paraffin waxes, microcrystalline waxes, polyolefin waxes and lecithin.
(6) The writing instrument as described in any of the above items (1) to (5), wherein a coating amount of the substance having a vaporization-inhibiting action is 0.01 to 20% by weight in terms of a weight ratio based on the pen tip.
(7) The writing instrument as described in any of the above items (1) to (6), wherein a content of the substance having a vaporization-inhibiting action is 0.01 to 10% by weight based on the total ink amount.
(8) The writing instrument as described in any of the above items (1) to (7), wherein the writing instrument comprises a knock type writing instrument needing no cap member, and operation of a knock part allows the pen tip comprising a fiber feeder or a plastic feeder in the inner pen to go forward from and backward into the writing instrument main body.